1. Field of the Invention
This invention relates to test indicators wherein a rotational displacement value of a measuring element is enlarged by a sector gear supported on a main body of the test indicator and transmitted to and indicated by an indicating device, and particularly to improvements in a mechanism for holding the measuring element at a neutral position.
2. Description of the Prior Art
The conventional test indicators have been generally of such an arrangement that a rotational displacement value of a measuring element is enlarged and transmitted to a hand through a sector gear and a transmission mechanism having a gear train operationally associated with the sector gear, and the rotational displacement value of the measuring element is read by use of the hand and a dial plate.
In the test indicators of the type described, in order to make the rotational displacement values of the measuring element in the normal and opposite directions equal to each other, it is necessary to arrange that, when the measuring element is held at substantially the center (i.e., the neutral position) of the scope of rotation thereof, the hand indicates the zero position of the dial plate. Heretofore, in order to obtain such a zero adjustment as described above, it has been proposed that, by pulling the sector gear toward opposite sides by use of two even tension springs, or by urging the sector gear from opposite sides by two sheet springs having urging forces equivalent in value to each other (according to Japanese Utility Model Application No. 59348/80), the sector gear is positioned at substantially the center of the scope of rotation thereof, to thereby hold the measuring element at a neutral position.
Nevertheless, even for the use of the even tension springs or the even-urging sheet springs, these springs have variabilities in resiliency to some extent and urging forces rendered to the sector gear by these springs are varied depending on the assembled conditions, thereby presenting the disadvantage that difficulties are encountered in achieving the adjustment described above.